We have discovered a new species of orangutan – the third known species and the first new great ape to be described since the bonobo almost a century ago.

The new species, called the Tapanuli orangutan (Pongo tapanuliensis), has a smaller skull than the existing Bornean and Sumatran orangutans, but has larger canines.

As we and our colleagues report in the journal Current Biology, the new species is represented by an isolated population of fewer than 800 orangutans living at Batang Toru in northern Sumatra, Indonesia.

Orangutan populations in Sumatra and Borneo – the new species’ distribution is shown in yellow.Curr. Biol.

The existence of a group of orangutans in this region was first reported back in 1939. But the Batang Toru orangutans were not rediscovered until 1997, and then confirmed in 2003. We set about carrying out further research to see whether this isolated group of orangutans was truly a unique species.

On the basis of genetic evidence, we have concluded that they are indeed distinct from both the other two known species of orangutan: Pongo abelii from further north in Sumatra, and Pongo pygmaeus from Borneo.

The Batang Toru orangutans have a curious mix of features. Mature males have cheek flanges similar to those of Bornean orangutans, but their slender build is more akin to Sumatran orangutans.

The hair colour is more cinnamon than the Bornean species, and the Batang Toru population also makes longer calls than other orangutans.

Making sure

To make completely sure, we needed more accurate comparisons of their body dimensions, or “morphology”. It was not until 2013 that the skeleton of an adult male became available, but since then one of us (Anton) has amassed some 500 skulls of the other two species, collected from 21 institutions, to allow for accurate comparisons.

Analyses have to be conducted at a similar developmental stage on male orangutan skulls, because they continue growing even when adult. Anton found 33 skulls of wild males that were suitable for comparison. Of 39 different measurement characteristics for the Batang Toru skull, 24 of them fall outside of the typical ranges of northern Sumatran and Bornean orangutans.

The new orangutans have smaller heads – but some impressive teeth.Matthew G Nowak, Author provided

Overall the Batang Toru male has a smaller skull, but bigger canines. Combining the genetic, vocal, and morphological sources of evidence, we have confidently concluded that Batang Toru orangutan population is a newly discovered species – and one whose future is already under threat.

Under threat as soon as they’re discovered.Maxime Aliaga, Author provided

Despite the heavy exploitation of the surrounding areas (hunting, habitat
alteration and other illegal activities), the communities surrounding the habitat of the Tapanuli orangutan still give us the opportunity to see and census the surviving population. Unfortunately, we believe that the population is fewer than 800 individuals.

Of the habitat itself, no more than 10 square km remains. Future development has been planned for that area, and about 15% of the orangutans’ habitat has non-protected forest status.

The discovery of the third orangutan in the 21st century gives us an understanding that the great apes have more diversity than we know, making it all the more important to conserve these various groups.

Without the strong support of, and participation from, the communities surrounding its habitat, the future of the Tapanuli orangutan will be uncertain. Government, researchers and conservation institutions must make a strong collaborative effort to make sure that this third orangutan will survive long after its discovery.

Scientists have described around 1.5 million species on Earth – but how many are still out there to be discovered? This is one of the most heated debates in biology. Discounting microbes, plausible estimates range from about half a million to more than 50 million species of unknown animals, plants and fungi.

This biodiversity matters because it could be used to fight human diseases, produce new crops, and offer innovations to help solve the world’s problems.

Why is there so much uncertainty in the numbers? The biggest reason, I argue, is that a lot of biodiversity is surprisingly hard to find or identify. This has profound implications for nature conservation and for our understanding of life on Earth.

Hidden biodiversity

We find new species every day but the organisms that we’re now discovering are often more hidden and more difficult to catch than ever before.

Not surprisingly, the first species to be described scientifically were big and obvious. The earliest naturalists to visit Africa, for instance, could hardly fail to discover zebras, giraffes and elephants.

Other unknown species are notoriously difficult to capture. For example, a biologist friend of mine was visiting his mother-in-law in north Queensland when her cat strolled in with an odd-looking animal in its mouth. He wrestled the cat’s dinner away and found that it was a mammal species never before seen in Australia called the prehensile-tailed rat.

Now known to be quite common in the Wet Tropics, this tree-dwelling rat almost never enters conventional wildlife traps. We can thank my mate’s mother-in-law’s cat for the discovery.

Other poorly explored places where new species wait to be discovered include the deep sea, soils and caves. After spending some 1,100 hours digging holes in the ground, biologists stumbled over the first species of Indian caecilian, a primitive, snake-like burrowing amphibian never before seen on the subcontinent.

On a far-flung beach in Alaska, a dead animal that washed ashore just last year turned out to be a completely new species of whale.

A frog species discovered in Borneo is the only frog in the world that completely lacks lungs. It lives in fast-flowing streams that are so oxygen-rich that it can breathe solely through its skin.

And a newly discovered spider in Morocco has evolved to move and escape predators by somersaulting over sand dunes.

The rainforest rooftop

High on the list of places to discover new species include rainforest canopies. In the early 1980s a Smithsonian Institution ecologist, Terry Erwin, used an insecticidal fog on several trees in the Panamanian rainforest and was stunned by his findings. Most of the insects that fell to the ground were entirely new species. Based on quick calculations he estimated that there could be 30 million species of insects residing in the canopies of the world’s rainforests.

Erwin’s conclusions, as it would be expressed today, went viral. In one fell swoop he had increased estimates of global biodiversity at least tenfold. Most biologists today consider his original estimate too high, however some believe he only overestimated a little.

Rainforest canopies are one of the world’s great biological frontiers.William Laurance

Cryptic species

Beyond species that are difficult to find or catch, a lot of unknown biodiversity is staring us right in the face but we simply can’t see it. For these species, new discoveries are down to advances in molecular genetics. Around 60% of all new organisms described today are so-called “cryptic species” that are nearly indistinguishable from one another.

In recent years, for example, we’ve discovered that Africa has not just one species of elephant but two. Formerly considered different subspecies, genetic analyses reveal that they’re as dissimilar to one another as the Asian elephant is to the extinct woolly mammoth.

Genetic studies have also revealed hidden variation among Africa’s giraffes. Just last year, researchers revealed that what was once considered a single species of giraffe is actually four.

Genetic studies have revealed that one apparent species of giraffe is actually four.William Laurance

Molecular genetics is turning biology on its head in other ways. Organisms we used to think were only distantly related, such as antelopes, dolphins and whales, are practically cousins in evolutionary terms.

Epicentres of unknown species

One last reason why many species are yet to be discovered is that they only live in a small area of the world. Known as “restricted endemics”, these species are geographically concentrated in certain regions such as tropical mountains, islands, and climatically unusual environments.

Most of Earth’s restricted endemics reside in “biodiversity hotspots”, defined by having more than 1,500 locally endemic plant species and less than 30% of their original habitat remaining. Of 35 currently recognised hotspots, half are in the species-rich tropics with the remainder divided among Mediterranean, islands and other ecosystems.

Today, the bulk of new species are being discovered in the biodiversity hotspots. The scary thing is that our recent analyses show that more than half of all hotspots have already lost over 90% of their intact habitat.

Further, most hotspots occur in poorer nations with rapidly-growing populations and escalating social and economic challenges, creating even greater pressures on their already beleaguered ecosystems and species.

Scary implications

Taken collectively, these studies suggest that there’s an enormous wealth of biodiversity on Earth left to discover and that much of it is in danger.

Further, our present knowledge is just scratching the surface. Evolution has had billions of years to create biologically active compounds that can combat human diseases, generate genetic diversity that could save our food crops from disastrous pathogens, and spawn ecological innovations that can inspire marvellous new inventions.

What a tragedy it would be to lose this biodiversity before we have ever had the chance to discover and learn from it.

A new species of Anglerfish discovered this year in the Gulf of Mexico. This bizarre fish has bioluminescent algae in the ‘fishing pole’ above its head to attract prey.Theodore W. Pietsch, University of Washington

We recently discovered 20 new species of fish in the Kimberley region of north-west Australia (one of them has been named after writer Tim Winton).

But that’s only the start of the story. At a time when the federal government is redoubling efforts to develop northern Australia, our discovery is a timely reminder of how little we know about our country.

A 2014 CSIRO report found 1.4 million hectares of land in northern Australia could be irrigated. Underlying this expansion would be approximately 90 large dams and numerous smaller water-regulating structures such as weirs.

The long-nosed sooty grunter is found in a single river in the Kimberley.Matthew Le Feuvre & James Shelley, Author provided

Threatened waterways

Fish are the most researched group of species living in Australia’s freshwater ecosystems. As such, we can use them as indicators of how much we know about these environments.

To date, research effort has been focused on south-east Australia. What stands out is a lack of research across much of the country, particularly in the north.

Despite this, northern Australia’s freshwater fish fauna is very diverse and includes many fish found across tiny areas. Unfortunately the lack of research means that for many of northern Australia’s fishes, all we know is that they exist.

Under the federal Environment Protection and Biodiversity Conservation (EPBC) Act, 16% of Australia’s freshwater fish are listed as threatened. But most of the species analysed are from the rivers of south-east Australia, which are most affected by people.

In a recent study we identified another 55 potentially vulnerable species that meet the criteria for conservation listing.

When we mapped the already listed and potentially vulnerable fish species, we found hotspots for fish conservation in the Kimberley, the Wet Tropics and Arnhem Land.

Map a) shows the number of currently listed threatened fish. Map b) shows the number of species that we identified as potentially vulnerable. Map c) shows river condition (1=best quality; 8=worst). Map shows d) freshwater fish research effort across Australia (red=most effort).Matthew Le Feuvre, Tim Dempster, James Shelley and Steve Swearer, Author provided

While often overlooked, Australia’s freshwater fish are almost as unique as our kangaroos and koalas: 74% of these fish are found nowhere else in the world.

Exploring the north

The Kimberley in northern Western Australia is rugged, remote, pristine and holds a number of species found nowhere else. We decided to investigate the region’s freshwater fishes.

Before our project began, we knew that the region was home to 50 species of freshwater fish, or almost a quarter of Australia’s freshwater fish species. Eighteen of these are found only in the Kimberley region.

Over the past three years, we spent nine months surveying over 70 sites on 17 of the Kimberley’s rivers. We found that many of the endemic species are potentially particularly vulnerable if their environment were to change. For example, the long-nosed sooty grunter is large, found in a single river, rare and exclusively carnivorous, making it vulnerable to extinction.

Excitingly, we also uncovered 20 new species of freshwater fish. This increases the known freshwater fish species in Australia by roughly 10% and, with 70 species in total, it makes the Kimberley the most diverse region for freshwater fish.

Many of the new species are large, clearly distinct fish, which could be identified as new species when we observed them from the riverbank. We found most of these new species in rivers we could only access by helicopter.

Put simply, due to the difficultly and expense of sampling the remote Kimberley wilderness, we just haven’t looked hard enough in the region’s rivers. Entire river systems in the Kimberley remain unsampled and we should not be surprised to uncover more species unknown to science.

What else is out there?

Our findings raise questions about the environmental sustainability of developing northern Australia. If we can find 20 new species of freshwater fish in nine months of fieldwork in the Kimberley, how many more species are present across the rest of northern Australia?

Fish are big and easy to find compared to most of the smaller aquatic life. They represent the conspicuous tip of the iceberg of what lives in our rivers. What happens if we investigate more cryptic or poorly known taxa such as amphibians or invertebrates?

How can we manage and protect species we don’t know exist? Before we develop the north, we need to know what’s out there.

The majority of northern rivers remain in relatively good condition, so there is ample opportunity to ensure that species are not lost as a result of development. Fortunately, most major developments are a decade or more away, so there is time to gather this information.

Learning from the south

Many rivers in southern Australia have been degraded by habitat modification, altered flow patterns, invasive species, barriers to fish movement, reduced water quality and overexploitation.

River flow, infrastructure and land use all need to be actively managed to maintain healthy rivers and allow key ecological processes, such as migrations and the inundation of floodplains, to continue. We need to be vigilant to prevent alien species invading.

A major source of conflict in the Murray-Darling Basin Plan was the allocation of water to the environment. Considering the environment as a stakeholder at the beginning of this process could have avoided future conflicts.

These practices will need to be adapted to the highly seasonal rainfall of northern Australia, which will be challenging. Intact rivers with particularly high numbers of species found nowhere else may be good candidates for freshwater protected areas, which are rare in Australia.

We need to ensure that our unique freshwater fishes are properly conserved. With research and good planning, we can ensure we do not repeat the sins of the past in northern Australia.